If adopted, the designation will prompt manufacturers either to phase out the substance’s use in that application or to undertake an alternatives analysis if they want to continue serving the California market.

Toluene is used as a solvent in a variety of nail products, including polishes, hardeners and thinners. But it has been linked with damage to the nervous system and respiratory tract, as well as developmental effects such as low birthweight. The DTSC said this presents concern for the state’s more than 130,000 nail salon workers, many of whom are women of childbearing age.

Meredith Williams, acting director of DTSC, said industry "has known for a long time that toluene is a problematic chemical in these products".

"Responsible manufacturers have moved away from it. We want to make sure that others do the same," she added.

As a first step, the DTSC has released a draft technical report outlining the scientific basis of the proposal. A comment period on the draft will be open until 15 March and the department will also host a public workshop to receive comments on 13 March. The technical report will then be updated, based on the comments, and submitted to an independent scientific review panel.

Toluene is also the subject of recent state-level legislation in states like New Jersey and New York, which are considering banning its use in nail products, alongside dibutyl phthalate (DBP) and formaldehyde.

In 2016, the DTSC sought feedback on this so-called "toxic trio" of substances. But in its technical report, it said that most nail product manufacturers have largely phased out formaldehyde and DBP, while some are continuing to use toluene.